Various kinds of torsion beam type suspension devices have been known as a rear suspension device of FF cars. This device comprises a pair of trailing arms fitted to right and left rear wheels, and a torsion beam to connect these trailing arms to each other. The trailing arms are pivotably supported by connecting a vibration isolating bush provided on a front end to a bracket of a car body in a rocking manner or by a toe-control link.
On the other hand, a wheel is supported rotatably by an axle fixed in the right-to-left direction of the car body through the fixed brackets at rear ends of the trailing arms. The brackets have been fixed to the trailing arms by welding or the like.
In recent years, the rear suspension device of high-class FF cars has been transferred from, so called, a rigid axle type and a torsion beam type to a double wishbone type or a multi-link type, and more sophisticated steering stability and ride quality performance have been demanded.
On the other hand, for example, in a rear suspension device of small FF cars of 1,500 cc class, no structure to sufficiently satisfy the characteristic requests for the steering stability and the ride quality performance has been available from the reasons of cost, weight and space. However, in recent year, a rear suspension device to satisfy the steering stability and the ride quality performance while satisfying the characteristic requests about cost, weight and space has been demanded even for the rear suspension device of FF cars of this class.
Further, various kinds of torsion beam axle type suspension devices have been known as rear suspension devices of compact to medium FF cars. These torsion beam axle type suspension devices comprises a pair of trailing arms 1001 fitted to right and left rear wheels 1005 through axle parts 1006 as illustrated in FIG. 29, and a torsion beam 1002 to connect these trailing arms 1001 to each other. The trailing arms 1001 are connected to a bracket 1004 on a car body (not shown) in a rocking manner through vibration isolating bushes 1003 provided on front ends. As shown in FIG. 28, the vibration isolating bushes 1003 is press-fitted in and fixed to a cylindrical opening part 1061 formed axially of an axle at front ends of the trailing arms, and in a structure thereof, a rubber elastic body 1054 of a predetermined thickness is vulcanization-bonded between outer cylinder 1053 and an inner cylinder 1052 which are concentric with each other. A suspension device having the vibration isolating bushes has a large number of advantages such as low cost, space saving and lightweightness.
However, this torsion beam axle type suspension device is basically connected to a car at two front end points of the pair of trailing arms, and the steering stability, the traveling stability, and the vibrational ride quality performance by vibration isolation bushes have been compatibly difficult. In other words, in the conventional torsion beam axle type suspension device, the toe change to the cornering force in the turn and to the braking force is in the toe-out trend on the turning outer wheel side, and is in a negative direction for the traveling stability of the car. In order to suppress the toe change, the rigidity of the vibration isolating bushes, in particular, the rigidity in the rotational direction around the transverse axis and the perpendicular axis has to be increased. On the other hand, from the aspect of the vibrational ride quality performance, it has been effective to reduce the rigidity, in particular, the rigidity in the longitudinal direction and the vertical direction. However, there has been a limit to satisfy every rigidity in each direction with the vibration isolating bushes at a pivot point, and each performance cannot be considerably improved, or performed compatibly.
Thus, an object of the present invention is to provide a torsion beam type suspension device to improve the steering stability and the ride quality performance without impairing characteristic requests about cost, weight and space.
Another object of the present invention is to provide an axle with rubber cushions for compatibly performing the steering stability, the traveling stability and the vibrational ride quality performance without impairing characteristic requests about cost, weight and space, and a torsion beam axle type suspension device using it.
Still another object of the present invention is to provide vibration isolating bushes for compatibly performing the steering stability, the traveling stability and the vibrational ride quality performance without impairing characteristic requests about cost, weight and space, and a torsion beam axle type suspension device using it.